I would argue that not warning them of what will happen if they miss the opportunity to transition with blockers is irresponsible given that it has been so devastating to so many trans adults. What they need is to have all the information so they can make informed choices.
Children cannot make informed choices about future fertility and sexual function of which they have no experience and no consideration of vs 'here's a magic solution to your dysmorphia right now'.
Clearly they therefore need protection from uninformed decisions by adults.
It's not a choice between an estrogen puberty and a testosterone puberty as you try to neatly obfuscate it.
It's a choice between a natural puberty which will allow for full fertility and sexual function if the dysmorphia resolves, but which will require a decision for synthetic hormones an surgery as an adult if it doesn't. which they as an adult can then decide.
Or, no puberty with a simulated late puberty with artificial hormones, lifelong medical treatment, extensive surgery, infertility and lack of full sexual function, even if happy with the decision, and no way back as an adult even if you're not.
When it boils down to it, the argument is really: these children will have more successful cosmetic surgery as adults if we give them puberty blockers now.